1. Field of the Invention
The present invention generally relates to a surface acoustic wave device and a method of fabricating the same, and more particularly, to a surface acoustic wave device suitably used for a filter device or an oscillator embedded in a television set (hereinafter referred to as TV), a video tape recorder (VTR), a digital video disk (DVD) player, a cellular phone or the like, and a method of fabricating such a device.
2. Description of the Related Art
Nowadays, the surface acoustic wave (SAW) device is widely used for various circuits that process radio frequency signals in the band of 45 MHz to 2 GHz. Examples of such circuits are a transmit band-pass filter, a receive band-pass filter, a local oscillation filter, an antenna duplexer, an intermediate frequency filter, and an FM modulator.
Recently, these devices for signal processing have been downsized, and it has been strongly demanded to downsize electronic components used therein including the SAW device. Particularly, the portable electronic devices such as cellular phones need a SAW device that allows face-down mounting and has a low package height.
FIG. 1 shows a conventional compact-size SAW device that is face-down mounted. A SAW device 900 has a SAW filter chip 901, which is flip-chip mounted in a container (also referred to as package) composed of a chip mounting base 921, an enclosure member 922, and a lit member 923. An on-board wiring or interconnection line 931 is provided on a surface of the chip mounting base 921 exposed to the cavity of the package (that surface being defined as an upper surface). The on-base interconnection line 931, which is positioned so as to correspond to bumps 911 of the SAW filter chip 901, is electrically connected thereto.
The on-board interconnection line 931 is electrically connected to a terminal 933 provided on the back surface of the chip mounting base 921 by a via interconnection 932 that penetrates through the chip mounting base 921. As is shown in FIG. 2, the terminal 933 is connected to an on-board wiring or interconnection line 942 provided on a parts mounting board 941 by a solder 943.
In many cases, the package that houses the SAW filter chip 901 is made of ceramics, as disclosed in Japanese Laid-Open Patent Application No. 7-336186.
It is required that the electronic parts mounted on the printed-circuit board are prevented from being broken due to bending of the board. As shown in FIG. 2, the SAW device 900 is tested by distorting the parts mounting board 941 on which the parts are fixed by soldering. This is called a board bending test.
Generally, the SAW filter chip used in the band of 800 MHz to 1.9 GHz employed in the cellular phone systems has a size smaller than 2 mm×2 mm. Thus, deforming of the package in the board bending test is ignorable, so that satisfactory reliability can be secured. However, the SAW filter chip used in the band of 30 MHz to 75 MHz in which the SAW device is used as the TV intermediate frequency filter has a size as large as 10 mm×2 mm. Thus, the board bending test deforms the package considerably. This results in large stress on the bump bonding via which the SAW filter chip is connected to the package. As is shown in FIG. 2, large stress may break joining of the bump 911 and the on-base interconnection line 931, and thus degrades the mounting reliability.